[STirish]

Hey guys,

There has been some kind of blanket correction with my A/F Learning since the rainy weather rolled in. The correction is there unless I'm getting into the gas (25%+ throttle) or I'm idling, after that the A/F Learning converges back to 7.8% correction. It's not surprising, but I would like to know what map(s) the correction may be coming from. This is really annoying to have weather like this when you're trying to tune

50-70 Deg F
30.3-30.5 inHg
100% Humidity

Am I the only one getting frustrated with unknown corrections?

Thanks,
Rob

[daemon]

We have learned so far that there is a coolant temp related fuel addition, but that is if it gets too hot I assume. It is also pretty certain than an increase in humidity creates a richer AFR due to the water displacing some of the oxygen for a given volume of air (or something like that). We also know that high IATs cause the ECU to pull timing (not related to a table I have seen I don't think). I do not know if high IATs cause extra fuel to be added since it already pulls timing because of it.

[STirish]

Originally Posted by daemon

We have learned so far that there is a coolant temp related fuel addition, but that is if it gets too hot I assume. It is also pretty certain than an increase in humidity creates a richer AFR due to the water displacing some of the oxygen for a given volume of air (or something like that). We also know that high IATs cause the ECU to pull timing (not related to a table I have seen I don't think). I do not know if high IATs cause extra fuel to be added since it already pulls timing because of it.

The higher the humidity, the lower the air density, correct? The car is pulling fuel, 7.8% of it.

Ok lets keep this going, I'll add the correction tbls/maps that I know:
WG DC:
Temp Correction: Add or subtract <= ??%
Barometric Correction: Add or subtract <= 50%

Thanks for the info...

[daemon]

Yeah. Increased humidity should be causing slightly richer conditions, not leaner. So if it is pulling fuel, then it must not be humidity. Where is it when it wasn't at 7.8%?

[daemon]

I'd love to know exactly how much humidity affects AFR. There should be a nice and simple mathematical formula that says at X% humidity the MAF will "miscalculate" the air flow by Y%. Are we talking off by up to 0.5 AFR from 0% to 100% humidity? More? Less? The ECU is supposed to eventually correct for humidity thanks to closed loop. How fast does this happen?

[STirish]

Originally Posted by daemon

Yeah. Increased humidity should be causing slightly richer conditions, not leaner. So if it is pulling fuel, then it must not be humidity. Where is it when it wasn't at 7.8%?

Yes, the humidity causes a rich condition in which the ECU responds to it by pulling fuel to get back to it's happy stoich during closed loop. I don't think the ECU knows of humidity, all it sees is the AFRs richening so it pulls fuel.

Originally Posted by daemon

I'd love to know exactly how much humidity affects AFR. There should be a nice and simple mathematical formula that says at X% humidity the MAF will "miscalculate" the air flow by Y%. Are we talking off by up to 0.5 AFR from 0% to 100% humidity? More? Less? The ECU is supposed to eventually correct for humidity thanks to closed loop. How fast does this happen?

We have been at ~100% humidity for the last 2.5 days or so where I have seen the A/F Learning be anywhere from 7.8-9.2% which I believe is also temperature dependent because that was the only measurable parameter changing during the weather. Pressure was fairly constant.

All in all I saw a change of about 0.5 AFR to now ~46% humidity. I was seeing 9.9-10.1 and now I'm seeing 10.3-10.5. I will be doing some tuning and logging tonight so I'll further get a feel for what the ECU has done.

[daemon]

Silly me. Yeah, that's what I meant to say. It's been a long day.